The Genetic Architecture of Skeletal Convergence and Sex Determination in Ninespine Sticklebacks

The history of life offers plentiful examples of convergent evolution, the independent derivation of similar phenotypes in distinct lineages. The emergence of convergent phenotypes among closely related lineages (frequently termed "parallel" evolution) is often assumed to result from changes in similar genes or developmental pathways, but the genetic origins of convergence remains poorly understood. Ninespine (Pungitius pungitius) and threespine (Gasterosteus aculeatus) stickleback fish provide many examples of convergent evolution of adaptive phenotypes, both within and between genera. The genetic architecture of several important traits is now known for threespine sticklebacks; thus, ninespine sticklebacks provide a unique opportunity to critically test whether similar or different chromosome regions control similar phenotypes in these lineages. We have generated the first genome-wide linkage map for ninespine sticklebacks and used quantitative trait locus mapping to identify chromosome regions controlling several skeletal traits and sex determination. In ninespine sticklebacks, these traits mapped to chromosome regions not previously known to control the corresponding traits in threespine sticklebacks. Therefore, convergent morphological evolution in these related, but independent, vertebrate lineages might have different genetic origins. Comparative genetics in sticklebacks provides an exciting opportunity to study the mechanisms controlling similar phenotypic changes in different animal groups.